The jasmonic acid-amino acid conjugates JA-Val and JA-Leu are involved in rice resistance to herbivores

The phytohormone jasmonic acid (JA) plays a core role in plant defence against herbivores. When attacked by herbivores, JA and its bioactive derivatives are accumulated at the damage site, and subsequently perceived by the jasmonate co-receptors COI1 and JAZ proteins. The (+)-7-iso-jasmonoyl-L-isoleucine (JA-Ile) is known to be the main active JA derivative controlling vascular plant responses to herbivores as well as other JA-regulated processes. However, whether other endogenous JA-amino acid conjugates (JA-AAs) are involved in herbivore-induced defence responses remain unknown. Here, we investigated the role of herbivore-elicited JA-AAs in the crop plant rice. The levels of five JA-AAs were significantly increased under the armyworm, leaf folder and brown planthopper attack. Of the elicited JA derivatives, JA-Ile, JA-Val and JA-Leu could serve as ligands to promote the interaction between rice COI1 and JAZs, inducing OsJAZ4 degradation in vivo. JA-Val or JA-Leu treatment increased the expression of JA- and defence-related pathway genes but not JA-Ile levels, suggesting that these JA-AAs may directly function in JA signalling. Furthermore, the application of JA-Val or JA-Leu resulted in JA-mediated plant growth inhibition, while enhancing plant resistance to herbivore attack. This study uncovers that JA-Val and JA-Leu also play a role in rice defence against herbivores.